Rotary lawn mowers in use today commonly comprise a motor-driven rotary blade which cuts grass into clippings as the mower is moved over the surface of a lawn. The clippings are then typically directed toward a grass catcher which collects the cut grass, or are dispersed directly onto the lawn. After mowing, the clippings are usually removed from the catcher, bagged, and disposed of as garbage. These bags filled with grass clippings comprise a large percentage of waste added to landfills each week. During the growing season, this percentage can be as high 50% in municipal landfills. In addition to creating added waste, the grass clippings carry lost fertilizer which must be replaced at added time and expense to the homeowner or landscaper.
Mulching lawn mowers have been developed in an attempt to alleviate the above-mentioned problems associated with discarded grass clippings. Mulching lawn mowers operate by cutting the grass clippings into fine particles which are returned into the lawn. The particles rapidly decompose, returning nitrogen and moisture to the soil and providing nutrients which fertilize the growing lawn. Furthermore, mulching mowers result in substantial savings in the time and effort required to mow the lawn, as the time-intensive chores of raking, bagging, and other clean-up of the cut grass are eliminated.
Optimum performance of mulching lawn mowers requires that the grass clippings be cut small enough to be deposited deep within the grass and soil below. In previous mowers, this was often attempted by using the vacuum created under the deck of the mower by the rotating blade to lift the cut grass clippings above the surface of the lawn where they are recut into small particles by the mower blade. However, previous rotary mulching mowers have not generated sufficient suction beneath the deck to keep the grass clippings suspended above the lawn. This results in much of the grass being cut only once, leaving behind large grass clippings on the surface of the lawn.
Some prior art mowers incorporate high-dome decks which redirect the cut grass particles over the top of the blade. However, in addition to the problems associated with poor vacuum, this type of design also creates random air flow pattern proximate the blade which can prevent grass clippings from being recut before falling to the ground. The shortcomings of prior mulching mowers are compounded when used on wet grass. Wet grass is often too heavy to be lifted by the minimal suction underneath the deck and, subsequently, is not cut by the rotary blade. As a result, manufactures have recommended that their mulching mowers only be used on dry grass.